Preheat the oven to 350 degrees F (175 degrees C).

Combine Dijon mustard, grainy mustard, honey, soy sauce, tarragon, and ginger in a large bowl.

Rinse chicken thighs under cold water and pat dry with paper towels.

Add chicken thighs to the bowl and toss to coat.

Transfer to a baking pan and spoon sauce over the thighs.

Bake in the preheated oven until chicken is no longer pink in the center and the juices run clear, about 45 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).

Spoon cooked sauce from the pan over chicken thighs before serving.